Sensor and device for detecting early fault of GIS electric connection structure and preparation method

Abstract

The invention discloses a sensor and device for detecting an early fault of a GIS electric connection structure and a preparation method. The sensor comprises a first single-mode optical fiber, a gas sensing optical fiber, a temperature sensing optical fiber and a second single-mode optical fiber which are connected in sequence, wherein the gas sensing optical fiber is of a structure formed by a single-mode optical fiber through high-temperature fused biconical taper, and is provided with an optical fiber taper part and an optical fiber waist area. An optical field in an optical fiber waist area is transmitted outside the optical fiber in an evanescent field mode, and the optical fiber waist area is coated with a metal organic framework material which is used for adsorbing and enriching characteristic products decomposed in the GIS. The aperture of the selected metal organic framework material is larger than the molecular size of each characteristic gas decomposed by SF6 in the GIS; the temperature sensing optical fiber is formed by writing a long-period optical fiber grating on a single-mode optical fiber, and the band-stop wavelength of the long-period optical fiber grating should avoid the absorption spectrum peak of gas to be detected in the GIS; according to the invention, synchronous detection of weak temperature rise and trace characteristic gas generated by early failure of the GIS electric connection structure can be realized.

Description

Technical Field

[0001] This invention belongs to the field of power equipment condition sensing, specifically relating to a sensor, device, and preparation method for detecting early faults in GIS electrical connection structures. Background Technology

[0002] Gas-insulated switchgear (GIS) plays a widely used role in modern power systems. The electrical connection structure, as a key component of GIS equipment, withstands high-density electromagnetic and thermal energy over extended periods, and is also affected by the reciprocating frictional mechanical loads caused by the thermal expansion and contraction of current-carrying conductors, thus requiring extremely high connection reliability. In recent years, GIS equipment failures caused by defects in the electrical connection structure or deterioration of contact performance have frequently occurred.

[0003] Various electrical connection structures exist within the gas chambers of GIS busbars, switchgear, etc., including fixed connections and plug-in connections. Fixed connections are mechanically secured using fasteners such as screws and rivets at the conductor connection points; plug-in connections rely on the elastic deformation force generated by the deformation of the contact fingers after the conductor is inserted to provide contact pressure, forming a non-fixed connection.

[0004] In terms of detection technology, existing methods have limitations such as low sensitivity, significant time lag, and insufficient fault correlation. Statistics in recent years have shown that conductor melting incidents caused by poor contact of GIS electrical connection structure and loose bolts occur frequently. No effective early warning signal was detected before the fault occurred, reflecting that it is difficult to provide timely early warning of GIS electrical connection defects by relying solely on existing conventional detection methods such as infrared thermometry, partial discharge detection, decomposition products, and shell vibration. The reasons are as follows: (1) Infrared thermometry of the shell is easily affected by external airflow, heat dissipation, light and ambient temperature, and the response to the temperature state of the internal electrical connection structure is lagging and sluggish. In the early stage of the fault, the shell temperature has almost no response to the temperature of the internal electrical connection of the GIS; (2) The offline detection cycle of SF6 decomposition products is long, and the time window of two samplings often exceeds the fault evolution characteristic time. The accuracy and anti-interference ability of the existing online monitoring technology are still insufficient, making it difficult to detect the weak gas concentration changes in the early stage of the fault in a timely and accurate manner. In addition, the frequent gas sampling also increases the risk of gas leakage; (3) The early fault characteristic signal is weak, and the early warning effect of a single sensing method is not good. Multiple monitoring methods should be combined for in-situ and synchronous analysis, which can improve the efficiency of early fault identification.

[0005] In summary, there is an urgent need to research in-situ and synchronous monitoring technologies for early-stage temperature and gas composition in electrical connection structures of GIS equipment. This would address the current lack of effective means for early-stage fault detection and maintenance assessment of electrical connection structures, and provide strong support for GIS equipment in terms of maintenance technology, operational equipment status awareness technology, and equipment technology. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a sensor, device, and preparation method for detecting early faults in GIS electrical connection structures. The present invention can achieve simultaneous detection of the slight temperature rise and trace characteristic gases generated by early faults in GIS electrical connection structures.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A sensor for detecting early faults in GIS electrical connection structures includes a first single-mode optical fiber, a gas sensing optical fiber, a temperature sensing optical fiber, and a second single-mode optical fiber connected in sequence. The gas sensing fiber includes a structure formed by high-temperature melting and tapering of single-mode fiber. This structure has a fiber waist region and fiber tapers at both ends of the fiber waist region. The fiber tapers at both ends of the fiber waist region are connected to a first single-mode fiber and a temperature sensing fiber, respectively. The volume sensing fiber also includes a metal-organic framework material coating layer on the surface of the fiber waist region. The metal-organic framework material coating layer is used to adsorb and enrich the characteristic products of decomposition inside GIS.

[0008] Preferably, the pore size of the metal-organic framework material coating layer is larger than the molecular size of the characteristic gases generated after the decomposition of SF6 inside the GIS.

[0009] Preferably, the thickness of the metal-organic framework material coating layer is between 50 nm and 200 nm.

[0010] Preferably, the metal-organic framework material cladding layer is a CUBTC type organic framework material.

[0011] Preferably, the temperature sensing fiber is constructed by writing a long-period fiber grating on a single-mode fiber, and the band-stop wavelength of the long-period fiber grating avoids the absorption spectral peak of the gas to be measured inside the GIS.

[0012] Preferably, the bandstop wavelength of the long-period fiber grating inscribed on the temperature sensing fiber is set to be 1 to 2 nm larger than the maximum wavelength of the spectral absorption peak of the characteristic gas to be measured.

[0013] Preferably, the bandstop wavelength of the long-period fiber grating is set to 1579–1580 nm.

[0014] The present invention also provides a method for preparing a sensor for detecting early faults in GIS electrical connection structures as described above, comprising the following steps: A single-mode optical fiber is subjected to high-temperature fusion tapering to form a gradually decreasing fiber taper and a fiber waist region located between the two fiber tapers. A metal-organic framework material cladding layer is prepared in the fiber waist region to obtain a gas sensing optical fiber. The large end of the fiber taper at one end of the gas sensing fiber is fused to one end of the first single-mode fiber, and the large end of the fiber taper at the other end of the gas sensing fiber is fused to one end of the temperature sensing fiber. The other end of the temperature sensing fiber is fused to one end of the second single-mode fiber, thus obtaining the sensor for detecting early faults in the GIS electrical connection structure.

[0015] Preferably, the metal-organic framework (MOF) cladding material is a CUBTC-type organic framework material, and the process of preparing the MOF cladding material in the fiber waist region specifically includes: Carboxyl groups are used as functional modifying groups to perform functional modification on the surface of the fiber waist region; The fiber waist region, after surface functional modification, is then immersed in a 3-aminopropyltriethoxysilane solution for 10-20 minutes, followed by immersion in succinic anhydride for 10-20 minutes to complete the carboxylation modification of the fiber waist region surface. Next, the fiber waist region is cyclically immersed in a Cu(CH3COO)2·H2O ethanol solution for 10-20 minutes, followed by immersion in a trimesic acid ethanol solution for 10-20 minutes, repeating the above immersion steps multiple times. By controlling the number of cycles, the thickness of the metal-organic framework cladding layer in the fiber waist region is controlled. In the Cu(CH3COO)2·H2O ethanol solution, the concentration of Cu(CH3COO)2·H2O is 0.25 mmol / L to 1 mmol / L; in the trimellitic acid ethanol solution, the concentration of trimellitic acid is 5 mmol / L to 10 mmol / L.

[0016] The present invention also provides an apparatus for detecting early faults in GIS electrical connection structures, comprising a broadband light source, a spectrometer, and a sensor for detecting early faults in GIS electrical connection structures as described above, wherein a first single-mode optical fiber is connected to the broadband light source, and a second single-mode optical fiber is connected to the spectrometer.

[0017] The present invention has the following beneficial effects: This invention relates to a sensor for detecting early faults in GIS electrical connection structures. Its core lies in the use of a composite structure of micro-nano optical fibers and fiber optic gratings to achieve synchronous and in-situ monitoring of characteristic gaseous products (including CO and H2S) and temperature associated with early GIS faults. The sensor mainly consists of a gas-sensing fiber and a temperature-sensing fiber. The gas-sensing fiber, through a surface-modified metal-organic framework material, adsorbs and enriches characteristic gases and utilizes the strong interaction between the fiber's evanescent field and the gas to generate spectral absorption. Gas content is detected by analyzing the absorption spectrum. The temperature-sensing fiber reflects temperature changes in real time. The gas-sensing and temperature-sensing fibers transmit signals through the same fiber optic link, ensuring strict spatial and temporal synchronization of monitoring data. Therefore, this invention's sensor for detecting early faults in GIS electrical connection structures offers the following advantages: 1. Enhanced diagnostic accuracy: In-situ monitoring avoids spatial errors inherent in traditional split-type sensors. Cross-validation eliminates environmental interference, improving the accuracy of early fault detection. 2. System integration and cost advantages: Using a single fiber optic link to transmit dual-parameter signals simplifies the wiring structure and reduces installation and maintenance costs. The sensor is small in size (approximately 200μm in diameter) and can be directly embedded inside GIS equipment without any additional modifications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the device for detecting early faults in the electrical connection structure of GIS according to the present invention.

[0019] Figure 2(a) is a schematic diagram of the gas sensing fiber in an embodiment of the present invention; Figure 2(b) is a schematic diagram of the structure of the waist region of the gas sensing fiber coated with metal-organic framework material in an embodiment of the present invention.

[0020] Figure 3 This is a light field distribution diagram of micro / nano optical fibers used in an embodiment of the present invention.

[0021] Figure 4 This is the sensor output spectrum diagram in an embodiment of the present invention.

[0022] Figure 5 This is a microstructure diagram of the fiber waist region of the gas sensing fiber prepared in the embodiments of the present invention, which is coated with metal-organic framework material.

[0023] In the figure, 1-first single-mode fiber, 2-gas sensing fiber, 2-1-fiber taper, 2-2-fiber waist region, 2-3-metal-organic framework cladding layer, 3-temperature sensing fiber, 4-second single-mode fiber, 5-broadband light source, 6-spectrometer. Detailed Implementation

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] See Figure 1 Figures 2(a) and 2(b) show that the sensor for detecting early faults in the electrical connection structure of the GIS in this embodiment includes a first single-mode fiber 1, a gas sensing fiber 2, a temperature sensing fiber 3, and a second single-mode fiber 4 connected in sequence. The main structure of the gas sensing fiber 2 is formed by fused taper of the single-mode fiber. The gas sensing fiber 2 has a fiber waist region 2-2 in the middle and fiber taper sections 2-1 at both ends of the fiber waist region 2-2. A metal-organic framework material cladding layer 2-3 is coated on the surface of the fiber waist region 2-2. The metal-organic framework material cladding layer 2-3 can adsorb and enrich the characteristic products of decomposition inside the GIS. The pore size of the selected metal-organic framework material cladding layer should be larger than the molecular size of the characteristic gas to be measured inside the GIS. The temperature sensing fiber 3 is obtained by writing a long-period fiber grating on the single-mode fiber. The band-stop wavelength of the long-period fiber grating should avoid the absorption spectral peak of the gas to be measured inside the GIS. Specifically, the band-stop wavelength of the long-period fiber grating is set to be 1-2 nm larger than the maximum wavelength of the spectral absorption peak of the characteristic gas to be measured. The main characteristic gas products detected by this invention for early GIS faults are CO and H2S. The near-infrared characteristic spectral absorption peaks of CO and H2S are 1567 nm and 1578 nm, respectively. Therefore, the preferred band-stop wavelength setting for the long-period fiber grating is 1579-1580 nm. Furthermore, since the molecular diameters of CO and H2S are 0.37 nm and 0.34 nm, respectively, a CUBTC-type organic framework material can be used. Its pore size can reach a maximum of 0.6 nm, and it has a very large specific surface area, enabling local enrichment of the gas and improving gas detection sensitivity. The sensor provided in this embodiment, by detecting the sensor's output spectrum and performing spectral information analysis, can achieve synchronous and in-situ analysis of characteristic gases and temperatures.

[0026] In this embodiment, the first single-mode fiber 1 and the temperature sensing fiber 3 are connected to the fiber taper regions 2-1 at both ends of the gas sensing fiber 2 by fusion splicing. The thickness of the metal-organic framework (MOF) cladding layer 2-3 covering the fiber waist region 2-2 is 50–200 nm to ensure sufficient adsorption of gas molecules and to guarantee the gas adsorption and dissociation rates (see Figure 2(b)). The pore size of the MOF cladding layer 2-3 should be larger than the molecular size of the characteristic gases to be measured inside the GIS (such as the characteristic gases produced after the decomposition of SF6), so that the characteristic gases in the GIS can enter the interior of the MOF through the pores. Due to the extremely high specific surface area of ​​the MOF, the gas molecules entering it will be enriched inside the MOF. The optical field of the fiber waist region 2-2 is transmitted in the form of an evanescent field. The evanescent field interacts strongly with the gas enriched inside the MOF, producing spectral absorption. By analyzing the intensity of the absorption spectrum, the concentration of fault characteristic gases inside the GIS can be monitored with high sensitivity.

[0027] In a preferred embodiment of the present invention, the diameter of the single-mode fiber used to process the gas sensing fiber 2 is 7μm to 10μm to ensure that the evanescent field of sufficient intensity completes the gas absorption detection.

[0028] This embodiment also provides a method for preparing a sensor for detecting early faults in GIS electrical connection structures provided in the above embodiments, including the following process: A single-mode optical fiber can be tapered at high temperature by hydrogen flame combustion to form an optical fiber tapered section 2-1 with gradually decreasing fiber diameter and an optical fiber waist region 2-2 located between the two optical fiber tapered sections 2-1. A metal-organic framework material cladding layer 2-3 is prepared in the optical fiber waist region 2-2 to obtain a gas sensing optical fiber 2. The large end of the fiber taper 2-1 at one end of the gas sensing fiber 2 is fused to one end of the first single-mode fiber 1, and the large end of the fiber taper 2-1 at the other end of the gas sensing fiber 2 is fused to one end of the temperature sensing fiber 3. The other end of the temperature sensing fiber 3 is fused to one end of the second single-mode fiber 4, thus obtaining the sensor for detecting early faults in the GIS electrical connection structure.

[0029] In a preferred embodiment of the present invention, the metal-organic framework material cladding layer 2-3 is made of CUBTC type organic framework material. The process of preparing the metal-organic framework material cladding layer 2-3 in the fiber waist region 2-2 specifically includes: The surface of the fiber waist region 2-2 was functionally modified using carboxyl groups (-COOH) as a modifying functional group; The fiber waist region 2-2, after surface functional modification, is immersed in 3-aminopropyltriethoxysilane solution (APTES) for 10-20 minutes, followed by immersion in succinic anhydride for 10-20 minutes to complete the carboxylation modification of the fiber waist region 2-2. Then, the fiber waist region 2-2 is repeatedly immersed in Cu(CH3COO)2·H2O ethanol solution for 10-20 minutes, followed by immersion in trimesic acid ethanol solution for 10-20 minutes, and the above immersion steps are repeated multiple times. By controlling the number of cycles, the thickness of the metal-organic framework material coating layer 2-3 in the fiber waist region is controlled. In the Cu(CH3COO)2·H2O ethanol solution, the concentration of Cu(CH3COO)2·H2O is 0.25 mmol / L to 1 mmol / L; in the pyromellitic acid ethanol solution, the concentration of pyromellitic acid is 5 mmol / L to 10 mmol / L.

[0030] Example See Figure 1 The device for detecting early faults in the electrical connection structure of GIS in this embodiment includes a broadband light source 5, a spectrometer 6, and a sensor for detecting early faults in the electrical connection structure of GIS as described in the above embodiment. One end of the first single-mode fiber 1 is connected to the broadband light source 5, and one end of the second single-mode fiber 4 is connected to the spectrometer 6. The broadband light source 5 is incident on one end of the first single-mode fiber 1. The other end of the single-mode fiber 1 is connected to a fiber taper 2-1 of a gas-sensing fiber 2 via fusion splicing. The fiber taper 2-1 at the other end of the gas-sensing fiber 2 is connected to one end of a temperature-sensing fiber 3, and the other end of the temperature-sensing fiber 3 is connected to the second single-mode fiber 4.

[0031] The surface of the fiber waist region 2-2 of the gas sensing fiber 2 is coated with metal-organic framework material CuBTC. The thickness of the metal-organic framework material CuBTC is 100 nm and the pore size is 0.6 nm. It is used to adsorb and enrich the characteristic products CO and H2S of the internal decomposition of GIS. The long-period fiber grating of the temperature sensing fiber 3 is set to 1580nm, which does not overlap with the near-infrared absorption peaks of the fault characteristic gas products CO and H2S. In the sensor output spectrum analysis, the gas and temperature information can be synchronously analyzed by separating the spectra. The bandwidth of the broadband light source 5 should cover the absorption wavelength of the gas under test and the bandstop wavelength of the long-period grating. In this embodiment, it is set to 1520-1600 nm.

[0032] The spectrometer 6 should have a spectral resolution of 20 pm and a dynamic range of 75 dB to achieve accurate analysis of temperature and gas content.

[0033] The working principle of this embodiment is as follows; The energy density of electromagnetic waves propagating along the axial (Z-direction) of a micro / nano fiber can be expressed using the Poynting vector. S z The time average is used to represent this. Therefore, the electromagnetic wave energy density distributions in the optical fiber and cladding can be obtained as follows: (1) In the formula: Z 0 — Wave impedance in free space , S z1 For the Poynting vector component in the optical fiber S z2 The Poynting vector component in the cladding. A The amplitude of the photoelectric field. J 0 is a zero-order Bessel function of the first kind. d The diameter of the optical fiber. r The radial distance of the optical fiber. K 0 represents a zero-order, abnormal Bessel function of the second kind. U This is the first characteristic parameter of the optical fiber. W This is the second characteristic parameter of the optical fiber.

[0034] right S z1 and S z2 Integrating the given electromagnetic wave energy distribution function across the cross-sections of the fiber and cladding respectively yields the power transmitted through the fiber and cladding. The ratio of the power transmitted within the fiber to the total power represents the transmission efficiency of the micro / nano fiber. η mf . η mf Characterizes the proportion of optical field energy confined within the optical fiber: (2) The input light wavelength is set to 1550nm, the center wavelength of the C-band communication band, and the refractive index of the optical fiber is... n 1 is 1.4646, and the cladding is air ( n By solving the above formulas (2~1.0), the transmission efficiency of micro / nano optical fibers with different fiber diameters can be obtained. η mf The value of increases with the increase of fiber diameter. η mf The value also increases, indicating that a larger proportion of the optical energy is confined inside the fiber. Conversely, the fiber diameter decreases. η mf The value decreases exponentially, and light energy is transmitted in the medium surrounding the optical fiber in the form of an evanescent field. The optical field transmission characteristics of micro / nano optical fibers are as follows: Figure 3 As shown, from Figure 3 It can be seen that in the waist region of micro-nano optical fibers, the light field is no longer confined to the inside of the fiber, but also exists in the air medium surrounding the fiber.

[0035] The pore size of the metal-organic framework (MOF) coating is larger than the molecular size of the characteristic gas to be measured inside the GIS. This allows the characteristic gas in the GIS to enter the MOF through the pores. Due to the extremely high specific surface area of ​​the MOF, the gas molecules inside will accumulate within the MOF, resulting in a local concentration much higher than the gas concentration in the environment, which is beneficial for enhancing gas sensing sensitivity. The optical field in the fiber waist region is transmitted in the form of an evanescent field. This evanescent field interacts strongly with the gas enriched inside the MOF, producing spectral absorption. According to the Beer-Lambert law: c =-ln(I / I0) / (A·L)(3) In the formula: I o For the incident light intensity, I The output light intensity is given by A, where A is the absorption constant of the gas being measured, and is a constant value. L This represents the effective interaction length between light waves and gas molecules. Therefore, by analyzing the intensity of the characteristic absorption peaks of the gas being measured in the sensor's output spectrum, the gas concentration can be determined. c Analysis.

[0036] To achieve simultaneous measurement of gas composition and temperature, a temperature sensing fiber is connected in series after the gas sensing fiber. Conventional Bragg fiber grating temperature measurements exhibit strong reflection spectra, which alias with the gas absorption spectrum, resulting in undecoupled spectral information. To address this, a long-period fiber grating with transmission spectral characteristics is used as the temperature-sensitive structure. Long-period fiber gratings exhibit transmission-type band-stop spectral characteristics; they have no spectral reflection, but their transmission spectrum exhibits transmission attenuation in a specific frequency band. The band-stop wavelength is: (2) In the formula, The core-mode propagation constant is denoted as . Let Λ be the cladding mode propagation constant, and Λ be the grating period. When the temperature changes, the grating period changes, causing a shift in the bandstop wavelength. By analyzing the shift in the bandstop wavelength of the transmission spectrum of a long-period grating, temperature information can be derived.

[0037] Sensor output spectrum such as Figure 4As shown, the output spectrum exhibits three attenuation peaks. The first attenuation peak is located at a wavelength of 1567 nm, and its power can be used to determine the CO gas concentration. The second attenuation peak is located at 1578 nm, and its power can be used to determine the H2S gas concentration. The third attenuation peak is located near 1579 nm, and its precise wavelength can be used to determine the temperature. This method enables the simultaneous and in-situ acquisition of characteristic gas CO, H2S, and temperature information generated by early faults in GIS electrical connection structures.

[0038] This embodiment also provides a typical fabrication method for a sensor for early failure of the above-mentioned GIS electrical connection structure, including the following process: A single-mode optical fiber is tapered at high temperature by hydrogen flame combustion to form a tapered section 2-1 with a gradually decreasing fiber diameter and a waist region 2-2 located between the two tapered sections. CuBTC metal-organic framework material was grown in the fiber waist region 2-2. This process involved functional modification of the fiber waist region using carboxyl groups (-COOH) as the modifying functional groups. The fiber was immersed in a 3-aminopropyltriethoxysilane (APTES) solution for 15 minutes, followed by immersion in succinic anhydride for 15 minutes to complete the carboxylation modification of the fiber surface. Then, the fiber was cyclically immersed in a Cu(CH3COO)2·H2O ethanol solution for 15 minutes, followed by immersion in a trimesic acid ethanol solution for 15 minutes. This process was repeated 30 times to coat the fiber waist region with a CuBTC metal-organic framework material with a thickness of approximately 100 nm. The concentration of Cu(CH3COO)2·H2O in the Cu(CH3COO)2·H2O ethanol solution was 1 mmol / L, and the concentration of trimesic acid in the trimesic acid ethanol solution was 5 mmol / L. Figure 5 Microstructure diagram of CuBTC grown in the waist region of optical fiber, from Figure 5 It can be seen that CuBTC is uniformly coated in the fiber waist region, the CuBTC film is defect-free, and has a high degree of structural uniformity.

[0039] Then, the large end of the tapered portion of one end of the gas sensing fiber 2 is fused to one end of the first single-mode fiber 1, the large end of the tapered portion of the other end of the gas sensing fiber 2 is fused to one end of the temperature sensing fiber 3, and the other end of the temperature sensing fiber 3 is fused to one end of the second single-mode fiber 4.

[0040] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A sensor for detecting early faults in GIS electrical connection structures, characterized in that, It includes a first single-mode fiber (1), a gas sensing fiber (2), a temperature sensing fiber (3), and a second single-mode fiber (4) connected in sequence. Among them, the gas sensing fiber (2) includes a structure formed by high-temperature melting and tapering of single-mode fiber. The structure has a fiber waist region (2-2) and fiber tapers (2-1) at both ends of the fiber waist region (2-2). The fiber tapers (2-1) at both ends of the fiber waist region (2-2) are connected to the first single-mode fiber (1) and the temperature sensing fiber (3) respectively. The gas sensing fiber (2) also includes a metal-organic framework material coating layer (2-3) on the surface of the fiber waist region (2-2). The metal-organic framework material coating layer (2-3) is used to adsorb and enrich the characteristic products of the decomposition inside GIS.

2. The sensor for detecting early faults in GIS electrical connection structures according to claim 1, characterized in that, The pore size of the metal-organic framework material coating layer (2-3) is larger than the molecular size of the characteristic gases produced after the decomposition of SF6 inside the GIS.

3. The sensor for detecting early faults in GIS electrical connection structures according to claim 1, characterized in that, The thickness of the metal-organic framework material coating layer (2-3) is between 50 nm and 200 nm.

4. A sensor for detecting early faults in GIS electrical connection structures according to any one of claims 1-3, characterized in that, The metal-organic framework material coating layer (2-3) is made of CUBTC type organic framework material.

5. The sensor for detecting early faults in GIS electrical connection structures according to claim 1, characterized in that, The temperature sensing fiber (3) is constructed by writing a long-period fiber grating on a single-mode fiber. The band-stop wavelength of the long-period fiber grating avoids the absorption spectrum peak of the gas to be measured inside the GIS.

6. A sensor for detecting early faults in GIS electrical connection structures according to claim 5, characterized in that, The band-stop wavelength of the long-period fiber grating inscribed on the temperature sensing fiber (3) is set to be 1-2 nm larger than the maximum wavelength of the spectral absorption peak of the characteristic gas to be measured.

7. A sensor for detecting early faults in GIS electrical connection structures according to claim 5 or 6, characterized in that, The bandstop wavelength of the long-period fiber grating is set to 1579–1580 nm.

8. A method for preparing a sensor for detecting early faults in GIS electrical connection structures according to any one of claims 1-7, characterized in that, The process includes the following: A single-mode fiber is subjected to high-temperature melting and tapering to form a fiber taper (2-1) with a gradually decreasing fiber diameter and a fiber waist region (2-2) located between the two fiber tapers (2-1). A metal-organic framework material cladding layer (2-3) is prepared in the fiber waist region (2-2) to obtain a gas sensing fiber (2). The large end of the fiber taper (2-1) at one end of the gas sensing fiber (2) is fused to one end of the first single-mode fiber (1), and the large end of the fiber taper (2-1) at the other end of the gas sensing fiber (2) is fused to one end of the temperature sensing fiber (3), and the other end of the temperature sensing fiber (3) is fused to one end of the second single-mode fiber (4) to obtain the sensor for detecting early faults in the GIS electrical connection structure.

9. A method for preparing a sensor for detecting early faults in GIS electrical connection structures according to claim 8, characterized in that, The metal-organic framework (2-3) cladding layer is made of CUBTC type organic framework material. The process of preparing the metal-organic framework (2-3) cladding layer in the fiber waist region (2-2) specifically includes: Carboxyl groups were used as functional groups to functionally modify the surface of the fiber waist region (2-2). The fiber waist region (2-2) after surface functional modification was then immersed in 3-aminopropyltriethoxysilane solution for 10-20 minutes, followed by immersion in succinic anhydride for 10-20 minutes to complete the carboxylation modification of the fiber waist region (2-2). Next, the fiber waist region (2-2) was repeatedly immersed in Cu(CH3COO)2·H2O ethanol solution for 10-20 minutes, followed by immersion in trimesic acid ethanol solution for 10-20 minutes. This immersion process was repeated multiple times. By controlling the number of cycles, the thickness of the metal-organic framework material coating layer (2-3) in the fiber waist region was controlled. In the Cu(CH3COO)2·H2O ethanol solution, the concentration of Cu(CH3COO)2·H2O is 0.25 mmol / L to 1 mmol / L; in the pyromellitic acid ethanol solution, the concentration of pyromellitic acid is 5 mmol / L to 10 mmol / L.

10. A device for detecting early faults in GIS electrical connection structures, characterized in that, The device includes a broadband light source (5), a spectrometer (6), and a sensor for detecting early faults in the electrical connection structure of a GIS as described in any one of claims 1-7, wherein a first single-mode fiber (1) is connected to the broadband light source (5), and a second single-mode fiber (4) is connected to the spectrometer (6).

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